Use of a sterically hindered aromatic amine or phenol compound as an anti-corrosion additive in a lubricant composition for a propulsion system of an electric or hybrid vehicle

ABSTRACT

The invention relates to the use of at least one compound, which has at least one sterically hindered amine or phenolic function, as an anti-corrosion additive in a lubricant composition for a propulsion system of an electric or hybrid vehicle, said lubricant composition comprising one or more amino and/or sulfur anti-wear additives. The invention also relates to the use of a lubricant composition comprising one or more compounds, which has at least one sterically hindered amine or phenolic function, as one or more anti-corrosion additives, further comprising one or more amino and/or sulfur anti-wear additives, for lubricating a propulsion system of an electric or hybrid vehicle, in particular for lubricating the electric motor and the power electronics of an electric or hybrid vehicle.

TECHNICAL FIELD

The present invention relates to the field of lubricant compositions for a propulsion system of an electric or hybrid vehicle. The invention more particularly relates to the use of compounds bearing at least one sterically hindered amine or phenol function for improving the anticorrosion properties of a lubricant composition incorporating one or more amine-based and/or sulfur-based antiwear additives.

The changes in the international standards for the reduction of CO₂ emissions, but also for the reduction of energy consumption, has driven motor vehicle constructors toward proposing alternative solutions to combustion engines.

One of the solutions identified by motor vehicle constructors consists in replacing combustion engines with electric motors. The research aimed at reducing CO₂ emissions has thus led to the development of electric vehicles by a certain number of motor vehicle companies.

For the purposes of the present invention, the term “electric vehicle” denotes a vehicle comprising an electric motor as sole means of propulsion, as opposed to a hybrid vehicle which comprises a combustion engine and an electric motor as combined means of propulsion.

For the purposes of the present invention, the term “propulsion system” denotes a system comprising the mechanical parts required for propelling an electric vehicle. The propulsion system thus more particularly encompasses an electric motor or the rotor-stator assembly of the power electronics (dedicated to regulating the speed), a transmission and a battery.

In general, it is necessary to use, in electric or hybrid vehicles, lubricant compositions, also known as “lubricants”, for the main purposes of reducing the friction forces between the various parts of the propulsion system of the vehicle, notably between the metal parts in motion in the motors. These lubricant compositions are also effective for preventing premature wear or even damage of these parts, and in particular of their surface.

To do this, a lubricant composition is conventionally composed of one or more base oils which are generally combined with several additives intended for stimulating the lubricant performance of the base oil, for instance friction-modifying additives, but also for affording additional performance.

In particular, “antiwear” additives are considered in order to reduce the wear of the mechanical parts of the motor, and thus to prevent degradation of the durability of the motor.

A wide variety of antiwear additives exists, among which mention may be made, for example, of dimercaptothiadiazoles, polysulfides, notably sulfur-based olefins, amine phosphates, or else phospho-sulfur additives, for instance metal alkylthiophosphates, in particular zinc alkylthiophosphates and more specifically zinc dialkyldithiophosphates or ZnDTP.

Among these antiwear additives, the ones that are notably favored are amine-based and/or sulfur-based antiwear agents, such as dimercaptothiadiazoles, zinc dithiophosphate or polysulfides.

Unfortunately, these amine-based and/or sulfur-based antiwear additives, such as dimercaptothiadiazoles, have the drawback of being corrosive. The problem of corrosion is particularly critical in electric propulsion systems. In particular, corrosion can lead to a risk of deterioration of the stator and rotor windings, the sensors in the propulsion system, the solenoid valves in the hydraulic system, but also of the rolling bearings between the rotor and stator of an electric motor, which are generally copper-based and thus particularly susceptible to corrosion, or to the seals or varnishes in the propulsion system.

The present invention is directed, specifically, towards overcoming this drawback.

In addition, in order to be able to cool the propulsion systems of electric or hybrid vehicles, it is essential that the lubricant be insulating in order to avoid any failure in the electrical components. In particular, a conductive lubricant can lead to a risk of electrical current leakage in the stator and rotor windings, which thus reduces the efficiency of the propulsion systems, and creates possible overheating of the electrical components, even to the point of damaging the system. In the context of using lubricants for electric or hybrid vehicle powertrain systems, it is thus crucial for the lubricants to have good “electrical” properties in addition to non-corrosive properties.

The present invention is specifically directed toward obtaining such properties

SUMMARY OF THE INVENTION

More precisely, the present invention relates to the use of at least one compound bearing at least one sterically hindered amine or phenol function, as an anticorrosion additive in a lubricant composition intended for a propulsion system of an electric or hybrid vehicle and comprising one or more amine-based and/or sulfur-based antiwear additives.

The compounds bearing at least one sterically hindered amine or phenol function, in particular bearing only one sterically hindered amine or phenol function, are referred to in the rest of the text as “compounds bearing a sterically hindered amine or phenol function”.

The compounds bearing a sterically hindered amine or phenol function, for instance hindered aromatic amines or phenols, notably alkylphenols, are already described for their function as antioxidants, for example in engine lubricants, as described, for example, in patent application WO 2006/064 138. These antioxidants generally make it possible to retard the degradation of the composition in service. This degradation may notably be reflected by the formation of deposits, the presence of sludges, or an increase in the viscosity of the composition. Antioxidants are capable of capturing the free radicals formed during the use of the lubricant, thus making it possible to interrupt the chain reactions liable to lead to the accumulation of acids.

To the inventors' knowledge, it has, however, never been proposed to use these compounds as anticorrosion additives in the context of using a lubricant for a propulsion system of an electric or hybrid vehicle, to overcome the corrosion effects brought about by the use of amine-based and/or sulfur-based antiwear additives.

Surprisingly, as illustrated in the example that follows, the inventors have found that such additives bearing a sterically hindered amine or phenol function, for example of diarylamine type, can efficiently reduce the corrosion effects induced by amine-based and/or sulfur-based antiwear additives.

Thus, the addition of at least one compound bearing a sterically hindered amine or phenol function, in particular of aromatic amine or alkylphenol type, can advantageously improve the anticorrosion properties of a lubricant composition comprising one or more amine-based and/or sulfur-based antiwear additives.

For the purposes of the present invention, the term “anticorrosion additive” denotes an additive for preventing or reducing the corrosion of metal parts. An anticorrosion additive used in a composition thus makes it possible to improve the “anticorrosion” properties of said composition.

The use of one or more compounds bearing a sterically hindered amine or phenol function according to the invention together with one or more amine-based and/or sulfur-based antiwear additives advantageously affords access to a lubricant composition which simultaneously has good antiwear performance, while at the same time overcoming the corrosion problems mentioned previously. A composition according to the invention thus simultaneously has good antiwear and anticorrosion properties.

The corrosive (or corroding) power of a compound may be evaluated by means of a test which studies the variation in the electrical resistance value of a copper w % ire of a preestablished diameter, as a function of the duration of immersion of this wire in a composition comprising said test compound in a noncorrosive medium, for example in one or more base oils. The variation in this electrical resistance value is directly correlated with the variation in the diameter of the test wire. Thus, in the context of the present invention, a compound is termed “noncorrosive” when the loss of diameter of the copper wire studied is less than or equal to 2 μm after immersion for 80 hours, in particular less than or equal to 0.3 μm after immersion for 20 hours in the composition comprising said compound.

The dielectric properties of a lubricant are notably represented by the electrical resistivity and the dielectric loss (tan δ) and may be measured according to the standard IEC 60247.

The electrical resistivity represents the capacity of a material to oppose the circulation of an electric current. It is expressed in ohm-metres (Ω.m). The resistivity must not be low to prevent electrical conduction.

The electric dissipation factor or the loss angle tangent also make it possible to measure the properties of a lubricant. The loss angle δ is the complementary angle δ f the phase shift between the applied voltage and the alternating current. This factor reflects the Joule-effect energy losses. Heating is thus directly linked to the δ value. A transmission oil typically has a tan δ value of the order of unity at ambient temperature. A good insulating lubricant must maintain a low tan δ level.

Advantageously, the compound bearing a sterically hindered amine or phenol function according to the invention used according to the invention is chosen from aromatic amines, in particular diarylamine compounds and more particularly diphenylamine compounds; sterically hindered phenols, in particular alkylphenols; and mixtures thereof.

According to a preferred embodiment, the compound bearing a sterically hindered amine or phenol function is chosen from substituted diphenylamines, which are in particular substituted on at least one of the positions para to the amine function with at least one alkyl or alkenyl group comprising from 1 to 12 carbon atoms, preferably from 3 to 10 carbon atoms.

By way of example, said compound may be p,p′-butyloctyldiphenylamine.

According to another preferred embodiment, the compound bearing a sterically hindered amine or phenol function is chosen from compounds comprising a phenol group, of which at least one carbon vicinal to the carbon bearing the alcohol function is substituted with at least one group chosen from an optionally substituted C₁-C₁₀ alkyl group and a hydroxyl function.

By way of example, said compound may be octyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate or 2,6-di-tert-butylphenol.

The introduction, into a lubricant composition intended for a propulsion system of an electric or hybrid vehicle, of one or more compounds bearing a sterically hindered amine or phenol function according to the invention thus advantageously permits the use, in the composition, of amine-based and/or sulfur-based antiwear additives, such as dimercaptothiadiazoles, without, however, entailing an adverse corrosive effect.

The amine-based and/or sulfur-based antiwear additives used in a lubricant composition according to the invention are more particularly detailed in the text hereinbelow. They are preferably chosen from amine-based and sulfur-based antiwear additives. They may preferably be thia(di)azole compounds, in particular dimercaptothiadiazole derivatives.

In addition, a composition that is suitable for use in the invention has the advantage of being easy to formulate. Besides good antiwear and anticorrosion performance, it has good stability, notably with respect to oxidation, and also good properties in terms of electrical insulation.

The present invention also relates to the use, for lubricating a propulsion system of an electric or hybrid vehicle, in particular for lubricating the electric motor and the power electronics of an electric or hybrid vehicle, of a lubricant composition comprising:

-   -   one or more compounds comprising at least one amine function or         a sterically hindered phenol function as defined in the         invention, as anticorrosion additive(s); and     -   one or more amine-based and/or sulfur-based antiwear additives         as defined in the invention.

A subject of the present invention is also a process for lubricating a propulsion system of an electric or hybrid vehicle, comprising at least one step of placing at least one mechanical part of said system in contact with a lubricant composition comprising at least one compound bearing a sterically hindered amine or phenol function as defined in the invention, as anticorrosion additive and at least one amine-based and/or sulfur-based antiwear additive as defined in the invention.

Advantageously, a lubricant composition according to the invention is used for lubricating the electric motor itself, in particular the rolling bearings located between the rotor and the stator of an electric motor, and/or the transmission, in particular the reducer, in an electric or hybrid vehicle.

Other features, variants and advantages of the use of compounds bearing a sterically hindered amine or phenol function as anticorrosion additives according to the invention will emerge more clearly on reading the description and the examples that follow, which are given as nonlimiting illustrations of the invention.

In the continuation of the text, the expressions “between . . . and . . . ”, “ranging from . . . to . . . ” and “varying from . . . to . . . ” are equivalent and are intended to mean that the limits are included, unless otherwise mentioned.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically represents a propulsion system of an electric or hybrid vehicle.

DETAILED DESCRIPTION Anticorrosion Additives Bearing a Sterically Hindered Amine Or Phenol Function

As stated previously, the additive used as anticorrosion agent according to the invention, together with one or more amine-based and/or sulfur-based antiwear additives, in a lubricant composition for the powertrain system of an electric or hybrid vehicle, is a compound bearing at least one sterically hindered amine or phenol function.

As mentioned previously, the compounds bearing a sterically hindered amine or phenol function, more particularly such as aromatic amines and hindered phenols, are known to those skilled in the art, in the field of lubricants, for their antioxidant action. These compounds are capable of acting as radical inhibitors.

The term “sterically hindered function” means that the function is hindered by a steric effect or constraint. The effect of this hindrance is to make the amine or phenol function significantly less nucleophilic than the unhindered amine or phenol function, and thus to prevent nucleophilic addition reactions.

Such compounds are described, for example, in patent applications WO 2006/064 138, WO 2011/073 960, etc.

However, as indicated previously, such compounds have never been proposed as anticorrosion additives in a lubricant for the powertrain system of an electric or hybrid vehicle, for the purposes of reducing or even inhibiting the corrosion effects induced by the use of one or more amine-based and/or sulfur-based antiwear additives.

The compounds bearing a hindered amine function may be chosen more particularly from aromatic amines, in particular as defined in the text hereinbelow.

The compounds bearing a hindered phenol function are preferably chosen from sterically hindered phenols, in particular alkylphenols, in particular as defined in the text hereinbelow.

Thus, according to a particular embodiment, said compound(s) bearing a hindered amine or phenol function are chosen from aromatic amines, sterically hindered phenols, and mixtures thereof.

In particular, the compounds of aromatic amine type may have the formula:

R₃R₄R₅N  [Chem 1]

in which R₃ and R₅ represent, independently of each other, a hydrogen atom, a C₁₋₂₀ and preferably C₄₋₁₆ aliphatic group, or an aromatic or heteroaromatic, monocyclic or fused polycyclic, substituted or unsubstituted group; R₅ is an aromatic or heteroaromatic, monocyclic or fused polycyclic group, which is unsubstituted or bears at least one C₁₋₂₀ alkyl substituent; or

R₃ and R₅ together form an aromatic or heteroaromatic, monocyclic or fused polycyclic group.

The aromatic amines may be chosen more particularly from substituted or unsubstituted diphenylamines, substituted or unsubstituted phenylnaphthylamines, substituted or unsubstituted phenothiazines, substituted or unsubstituted imidodibenzyls, substituted or unsubstituted N,N′-diphenyl(phenylenediamines), and mixtures thereof.

According to a particularly preferred embodiment, the compounds bearing a hindered amine function are chosen from secondary amines in which the nitrogen atom is linked to at least one aryl group, preferably to at least one phenyl group.

Preferably, the compound bearing a hindered amine function is chosen from diarylamine compounds, in particular in which at least one of the aryl groups is a phenyl, and more particularly diphenylamine compounds.

Thus, according to a particular embodiment, the compound bearing a hindered amine function is a compound of aromatic amine type chosen from diarylamines, preferably corresponding to the formula.

R₆NH—R₇  [Chem 2]

in which R₆, and R₇ are chosen, independently of each other, from:

-   -   a phenyl group, which is optionally substituted, preferably para         to the amine function, with hydrocarbon-based groups, in         particular chosen from alkyl or alkenyl groups comprising from 1         to 12 carbon atoms, preferably from 3 to 10 carbon atoms; and     -   a naphthyl group, which is optionally substituted, preferably         para to the amine function, with hydrocarbon-based groups, in         particular chosen from alkyl or alkenyl groups comprising from 1         to 12 carbon atoms, preferably from 3 to 10 carbon atoms.

Advantageously, the compound bearing a hindered amine or phenol function is chosen from diphenylamine compounds, which are preferably substituted, in particular substituted on at least one of the positions para to the amine function with at least one alkyl or alkenyl group comprising from 1 to 12 carbon atoms, preferably from 3 to 10 carbon atoms.

In other words, the compound bearing a hindered amine function may advantageously be of formula (I) below:

in which R₁ and R₂ are chosen, independently of each other, from a hydrogen atom, linear or branched alkyl or alkenyl groups, preferably alkyl groups, comprising from 1 to 12 carbon atoms, preferably from 3 to 10 carbon atoms.

According to a particular embodiment, the compound bearing a hindered amine function is of the abovementioned formula (I), in which at least one from among R₁ and R₂ is a linear or branched alkyl or alkenyl group, preferably an alkyl group, comprising from 1 to 12 carbon atoms, preferably from 3 to 10 carbon atoms.

Preferably, said compound is of the abovementioned formula (I), in which R₁ and R₂ are chosen, independently of each other, from linear or branched alkyl or alkenyl groups, preferably alkyl groups, comprising from 1 to 12 carbon atoms, preferably from 3 to 10 carbon atoms.

Preferably, R₁ and R₂ are in the para position relative to the amine function.

In other words, the compound bearing a hindered amine function may advantageously be of formula (I′):

in which R₁ and R₂ are as defined previously.

Advantageously, R₁ and R₂, which may be identical or different, represent linear or branched C₁ to C₁₂ and preferably C₃ to C₁₀ alkyl groups, for example chosen from linear or branched octyl and butyl groups.

The compounds bearing a hindered amine function may be commercially available or prepared according to synthetic methods known to those skilled in the art.

By way of example, mention may be made of p,p′-butyloctyldiphenylamine.

The compounds bearing a hindered amine or phenol function may also be compounds of sterically hindered phenol type.

The compounds of sterically hindered phenol type are preferably compounds including a phenol group, of which at least one carbon atom other than the one bearing the hydroxyl function and forming part of the phenyl group bears a hydroxyl radical, a linear or branched C₁₋₁₀ alkyl, a dialkylaminoalkyl group or a styryl group.

Preferably, the sterically hindered phenols are chosen from compounds comprising a phenol group, in which at least one carbon vicinal to the carbon bearing the alcohol function is substituted with at least one group chosen from a C₁-C₁₀ alkyl group and a hydroxyl function. In other words, the compound bearing a hindered phenol function may be a sterically hindered phenol of formula (II) below:

in which:

at least one from among R₁ and R₂ represents a C₁-C₁₀ alkyl group, preferably a C₁-C₆ alkyl group, preferably a C₄ alkyl group, for example tert-butyl; or a hydroxyl group;

the carbon atoms of the benzene ring, other than those bearing the groups R¹, R² and OH, being optionally substituted.

In particular, the compound bearing a hindered phenol function may be of formula (II′) below:

in which:

at least one from among R₁ and R₂ represents a C₁-C₁₀ alkyl group, preferably a C₁-C₆ alkyl group, preferably a C₄ alkyl group, for example tert-butyl; or a hydroxyl group;

n being an integer between 0 and 3:

R being chosen, independently of each other, from C₁-C₁₀ alkyl groups, optionally substituted with one or more C₂ to C₁₀ alkoxycarbonyl groups such as an octyloxycarbonyl group and/or with one or more aryl groups, the aryl group(s) themselves being optionally substituted with one or more alkyl groups; and a hydroxyl group.

As examples of compounds of sterically hindered phenol type, mention may be made of 2,6-di-t-butyl-4-methylphenol (BHT), t-butylhydroquinone (TBHQ), 2,6- and 2,4-di-t-butylphenol, 2,4-dimethyl-6-t-butylphenol, pyrogallol and octyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, alone or as a mixture.

Preferably, the compound of sterically hindered phenol type is chosen from “alkylphenol” compounds, comprising a phenol group bearing on at least one of the positions ortho to the hydroxyl function, preferably on both the ortho positions, a sterically hindered alkyl group, preferably of C₁ to C₁₀, in particular C₁-C₆, in particular a C₄ alkyl group, preferably tert-butyl.

In particular, it may be a compound of the abovementioned formula (II), in particular of the abovementioned formula (II′), in which at least one from among R¹ and R², or even both the groups R¹ and R², are chosen from C₁-C₁₀ alkyl groups, preferably C₁-C₆ alkyl groups, preferably a C₄ alkyl group, preferably tert-butyl.

The compounds bearing a hindered phenol function may be commercially available or prepared according to synthetic methods known to those skilled in the art.

As examples of preferred compounds of sterically hindered phenol type, mention may be made of octyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate or 2,6-di-tert-butylphenol. An example of an even more preferred compound of sterically hindered phenol type that may be mentioned is octyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate.

According to a preferred embodiment, the compound of sterically hindered aromatic amine or phenol type is chosen from p,p′-butyloctyldiphenylamine, octyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, 2,6-di-tert-butylphenol, and mixtures thereof.

According to an even more preferred embodiment, the compound of sterically hindered aromatic amine or phenol type is chosen from p,p′-butyloctyldiphenylamine, octyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, and mixtures thereof.

The invention is not limited to the compounds of hindered aromatic amine or phenol type described above. Other compound bearing a sterically hindered amine or phenol function, notably known as antioxidants, may be used as anticorrosion additives according to the invention.

In the context of the invention, the following definitions apply:

-   -   “alkyl”: a linear or branched, saturated aliphatic group; for         example, a C_(x) to C_(y) alkyl represents a linear or branched         hydrocarbon-based chain of x to y carbon atoms;     -   “alkenyl”: a linear or branched, unsaturated aliphatic group;         for example, a C_(x) to C_(y) alkenyl group represents a linear         or branched unsaturated carbon-based chain of x to y carbon         atoms;     -   “alkoxy”: a radical —O-alkyl, in which the alkyl group is as         defined previously;     -   “aryl”: a monocyclic or polycyclic aromatic group in particular         comprising between 5 and 10 carbon atoms. Examples of aryl         groups that may be mentioned include phenyl, tolyl and naphthyl         groups.

Advantageously, said compound(s) bearing a sterically hindered amine or phenol function used according to the invention are chosen from:

-   -   aromatic amines, in particular as described previously, notably         diarylaromatic amines, and more particularly diphenylamines,         which are preferably substituted, advantageously in the para         position relative to the amine function, with at least one         C₁-C₁₂ alkyl group.     -   sterically hindered phenols, in particular as defined         previously, and preferably compounds comprising a phenol group,         in which at least one carbon vicinal to the carbon bearing the         alcohol function is substituted with at least one C₁-C₁₀,         preferably C₁-C₆ and notably C₄ alkyl group, in particular         tert-butyl; and     -   mixtures thereof.

It is understood, in the context of the present invention, that a compound bearing a sterically hindered amine or phenol function may be in the form of a mixture of at least two compounds bearing a sterically hindered amine or phenol function, for example a mixture of at least one compound bearing a sterically hindered amine function and of at least one compound bearing a sterically hindered phenol function.

The compound(s) bearing a sterically hindered amine or phenol function, in particular as defined previously, may be used in a lubricant composition according to the invention in a proportion of from 0.01% to 5% by mass, in particular from 0.1% to 3% by mass and more particularly from 0.1% to 1% by mass relative to the total mass of the lubricant composition.

Advantageously, a lubricant composition under consideration according to the invention does not comprise any anticorrosion additives other than the compounds bearing a sterically hindered amine or phenol function. According to a particular embodiment, a lubricant composition used according to the invention is free of anticorrosion additives of triazole type or of succinimide type.

Lubricant Composition

Amine-Based and/or Sulfur-Based Antiwear Additives

As indicated previously, a lubricant composition under consideration according to the invention comprises one or more amine-based and/or sulfur-based antiwear additives.

The term “amine-based and/or sulfur-based antiwear additive” denotes an additive chosen from amine-based antiwear additives, sulfur-based antiwear additives and amine-based and sulfur-based antiwear additives.

The term “antiwear additive” denotes a compound which, when used in a lubricant composition, notably a lubricant composition for a propulsion system of an electric or hybrid vehicle, makes it possible to improve the antiwear properties of the composition.

The amine-based and/or sulfur-based antiwear additive may be chosen, for example, from additives of thia(di)azole type, in particular dimercaptothiadiazole derivatives; polysulfide additives, notably sulfur-based olefins, amine phosphates, phospho-sulfur additives such as alkylthiophosphates, and mixtures thereof.

Thia(Di)Azole Additives

According to a particularly preferred embodiment, a lubricant composition under consideration according to the invention comprises at least one thia(di)azole antiwear additive.

Thia(di)azole compounds are compounds which contain both a sulfur atom and at least one nitrogen atom in a five-atom ring. Benzothiazoles are a particular type of thia(di)azoles. This term “thia(di)azole” includes, besides cyclic compounds containing one sulfur atom and one nitrogen atom per five-atom ring, also thiadiazoles which contain sulfur and two nitrogen atoms in such a ring.

In particular, the thia(di)azole compounds may be chosen from benzothiazole derivatives, thiazole derivatives and thiadiazole derivatives.

Preferably, the antiwear additive may be a thiadiazole derivative.

Thiadiazoles are heterocyclic compounds comprising two nitrogen atoms, one sulfur atom, two carbon atoms and two double bonds, of general formula C₂N₂SH₂, which may exist in the following forms, respectively: 1,2,3-thiadiazole; 1,2,4-thiadiazole; 1,2,5-thiadiazole; 1,3,4-thiadiazole:

Preferably, the thiadiazole derivative is a dimercaptothiadiazole derivative.

Thus, according to a particularly preferred embodiment, a lubricant composition according to the invention comprises at least one antiwear additive chosen from dimercaptothiazole derivatives.

The term “dimercaptothiadiazole derivative” according to the invention means chemical compounds derived from the following four dimercaptothiadiazole molecules below: 4,5-dimercapto-1,2,3-thiadiazole, 3,5-dimercapto-1,2,4-thiadiazole, 3,4-dimercapto-1,2,5-thiadiazole, 2,5-dimercapto-1,3,4-thiadiazole, taken alone or as a mixture:

The dimercaptothiadiazole derivatives are more particularly molecules or a mixture of molecules based on 4,5-dimercapto-1,2,3-thiadiazole, 3,5-dimercapto-1,2,4-thiadiazole, 3,4-dimercapto-1,2,5-thiadiazole or 2,5-dimercapto-1,3,4-thiadiazole, as represented above, in which at least one of the substitutions ═S, or even both substitutions ═S on the thiadiazole ring is replaced with a substituent:

in which * represents the bond with a carbon atom of the 5-membered ring, n represents an integer equal to 1, 2, 3 or 4; and R₁ is chosen from a hydrogen atom, a linear or branched, saturated or unsaturated alkyl group comprising from 1 to 24, preferably from 2 to 18, more preferentially from 4 to 16 and even more preferentially from 8 to 12 carbon atoms or an aromatic substituent.

In particular, taking 2,5-dimercapto-1,3,4-thiadiazole as example, the 2,5-dimercapto-1,3,4-thiadiazole derivatives are molecules having the following formulae, taken alone or as a mixture:

in which the group(s) R₁ represent, independently of each other, hydrogen atoms, linear or branched alkyl or alkenyl groups comprising from 1 to 24, preferably from 2 to 18, more preferentially from 4 to 16 and even more preferentially from 8 to 12 carbon atoms or aromatic substituents, n being, independently of each other, integers equal to 1, 2, 3 or 4, n preferably being equal to 1.

Preferably, R₁ represent, independently of each other, linear C₁ to C₂₄, preferably C₂ to C₁₈, notably C₄ to C₁₆, more particularly C₈ to C₁₂ and preferably C₁₂ alkyl groups.

The dimercaptothiadiazole derivatives used in the present invention may be commercially available, for example from the suppliers Vanderbilt, Rhein Chemie or Afton.

Polysulfide Additives

The amine-based and/or sulfur-based antiwear additive(s) used in a lubricant composition according to the invention may also be chosen from sulfur-based antiwear additives of polysulfide type, in particular sulfur-based olefins.

The sulfur-based olefins used in a lubricant composition according to the invention may notably be dialkyl sulfides represented by the general formula R_(a)—S_(x)—R_(b), in which R_(a) and R_(b) are alkyl groups including from 3 to 15 carbon atoms, preferentially from 1 to 5 carbon atoms, preferentially 3 carbon atoms, and x is an integer between 2 and 6.

Preferably, the polysulfide additive is chosen from dialkyl trisulfides.

Preferably, the antiwear additive present in a composition used according to the invention is chosen from amine-based and sulfur-based antiwear additives, and advantageously from thia(di)azole compounds as described above and more preferentially from dimercaptothiadiazole derivatives.

A lubricant composition under consideration according to the invention may comprise from 0.01% to 5% by mass, in particular from 0.1% to 3% by mass and more particularly from 0.1% to 1% by mass of amine-based and/or sulfur-based antiwear additive(s), preferably of thia(di)azole type and more preferentially chosen from dimercaptothiadiazole derivatives.

The use of other antiwear additives, notably known for lubricants for propulsion systems, other than amine-based and/or sulfur-based additives, is envisageable, provided that they do not affect the properties imparted by the combination of said compound(s) bearing a sterically hindered amine or phenol function and of said amine-based and/or sulfur-based antiwear additive(s) according to the invention.

Preferably, a lubricant composition required according to the invention is free of antiwear additives other than said amine-based and/or sulfur-based antiwear additive(s) used according to the invention.

According to a particularly preferred embodiment, a lubricant composition under consideration according to the invention combines:

-   -   one or more compounds bearing a sterically hindered amine or         phenol function, in particular chosen from:     -   aromatic amines, in particular as described previously, notably         diarylaromatic amines, and more particularly diphenylamines,         which are preferably substituted, advantageously in the para         position relative to the amine function, with at least one         C₁-C₁₂ alkyl group;     -   sterically hindered phenols, in particular as defined         previously, and preferably compounds comprising a phenol group,         in which at least one carbon vicinal to the carbon bearing the         alcohol function is substituted with at least one C₁-C₁₀,         preferably C₁-C₆ and notably C₄ alkyl group, in particular         tert-butyl;         and mixtures thereof; and     -   one or more amine-based and sulfur-based antiwear additives,         preferably chosen from dimercaptothiazole derivatives, in         particular as defined above.

A composition used according to the invention may comprise, besides one or more additives bearing a sterically hindered amine or phenol function and one or more amine-based and/or sulfur-based antiwear additives, in particular as defined previously, one or more base oils, and also other additives, conventionally considered in lubricant compositions.

Base Oil

A lubricant composition under consideration according to the invention may thus comprise one or more base oils.

These base oils may be chosen from the base oils conventionally used in the field of lubricant oils, such as mineral, synthetic or natural, animal or plant oils or mixtures thereof.

It may be a mixture of several base oils, for example a mixture of two, three or four base oils.

The base oils of the lubricant compositions under consideration according to the invention may in particular be oils of mineral or synthetic origin belonging to groups I to V according to the classes defined in the API classification (or equivalents thereof according to the ATIEL classification) and presented in Table 1 below or mixtures thereof.

TABLE 1 Content of saturates Sulfur content Viscosity index (VI) Group 1 <90% >0.03% 80 ≤ VI < 120 Mineral oils Group II ≥90% ≤0.03% 80 ≤ VI < 120 Hydrocracked oils Group III ≥90% ≤0.03% ≥120 Hydrocracked or hydroisomerized oils Group IV Poly-α-olefins (PAO) Group V Esters and other bases not included in groups I to IV

The mineral base oils include all types of base oils obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, deasphalting, solvent deparaffinning, hydrotreating, hydrocracking, hydroisomerization and hydrofinishing.

Mixtures of synthetic and mineral oils, which may be biobased, may also be used.

There is generally no limit as regards the use of different base oils for preparing the compositions used according to the invention, other than the fact that they must have properties, notably in terms of viscosity, viscosity index or resistance to oxidation, that are suitable for use for the propulsion systems of an electric or hybrid vehicle.

The base oils of the compositions used according to the invention may also be chosen from synthetic oils, such as certain esters of carboxylic acids and of alcohols, poly-α-olefins (PAO) and polyalkylene glycols (PAG) obtained by polymerization or copolymerization of alkylene oxides comprising from 2 to 8 carbon atoms, in particular from 2 to 4 carbon atoms. The PAOs used as base oils are obtained, for example, from monomers comprising from 4 to 32 carbon atoms, for example from octene or decene. The weight-average molecular mass of the PAO may vary quite broadly. Preferably, the weight-average molecular mass of the PAO is less than 600 Da. The weight-average molecular mass of the PAO may also range from 100 to 600 Da, from 150 to 600 Da or from 200 to 600 Da.

Advantageously, the base oil(s) of the composition used according to the invention are chosen from poly-α-olefins (PAO), polyalkylene glycols (PAG) and esters of carboxylic acids and of alcohols.

According to an alternative embodiment, the base oil(s) of the composition used according to the invention may be chosen from group II or III base oils.

It falls to a person skilled in the art to adjust the content of base oil to be used in a composition that is suitable for use in the invention.

A lubricant composition under consideration according to the invention may comprise at least 50% by mass of base oil(s) relative to its total mass, in particular from 60% to 99% by mass of base oil(s), relative to its total mass.

Additional Additives

A lubricant composition that is suitable for use in the invention may also comprise any type of additive, different from the additives bearing a sterically hindered amine or phenol function and from the amine-based and/or sulfur-based antiwear additives defined in the context of the present invention, that are suitable for use in a lubricant for a propulsion system of an electric or hybrid vehicle.

It is understood that the nature and amount of additives used are chosen so as not to affect the properties in terms of antiwear and anticorrosion performance imparted by the combination of said compound(s) bearing a sterically hindered amine or phenol function and of said amine-based and/or sulfur-based additive(s) used according to the invention.

Such additives, which are known to a person skilled in the art in the field of the lubrication and/or cooling of the propulsion systems of electric or hybrid vehicles, may be chosen from friction modifiers, detergents, extreme-pressure additives, antifoams, pour-point depressant additives, dispersants, antioxidants other than the compounds bearing a sterically hindered amine or phenol function according to the invention, pour-point depressants, antifoams and mixtures thereof.

Advantageously, a composition that is suitable for use in the invention comprises at least one additional additive chosen from friction modifiers, detergents, extreme-pressure additives, antifoams, pour-point depressant additives, dispersants, antioxidants other than the compounds bearing a sterically hindered amine or phenol function according to the invention, and mixtures thereof.

These additives may be introduced individually and/or in the form of a mixture such as those already available for sale for commercial lubricant formulations for vehicle engines, with a performance level as defined by the ACEA (Association des Constructeurs Européens d'Automobiles) and/or the API (American Petroleum Institute), which are well known to those skilled in the art.

A lubricant composition that is suitable for use in the invention may comprise at least one friction-modifying additive. The friction-modifying additive may be chosen from a compound providing metal elements and an ash-free compound. Among the compounds providing metal elements, mention may be made of complexes of transition metals such as Mo, Sb, Sn, Fe, Cu or Zn, the ligands of which may be hydrocarbon-based compounds comprising oxygen, nitrogen, sulfur or phosphorus atoms. The ash-free friction-modifying additives are generally of organic origin and may be chosen from fatty acid monoesters of polyols, alkoxylated amines, alkoxylated fatty amines, fatty epoxides, borate fatty epoxides, fatty amines or fatty acid esters of glycerol. According to the invention, the fatty compounds comprise at least one hydrocarbon-based group comprising 10 to 24 carbon atoms.

A lubricant composition that is suitable for use according to the invention may comprise from 0.01% to 2% by weight or from 0.01% to 5% by weight, preferentially from 0.1% to 1.5% by weight or from 0.1% to 2% by weight of friction-modifying additive, relative to the total weight of the composition.

A lubricant composition used according to the invention may comprise at least one antioxidant additive different from the compounds bearing a sterically hindered amine or phenol function as defined according to the invention.

The antioxidant additive generally makes it possible to retard the degradation of the composition in service. This degradation may notably be reflected by the formation of deposits, the presence of sludges, or by an increase in the viscosity of the composition.

The antioxidant additives notably act as free-radical inhibitors or hydroperoxide destroyers. Antioxidant additives different from the compounds bearing a sterically hindered amine or phenol function may be, for example, copper compounds, for example copper thio- or dithio-phosphates, copper salts of carboxylic acids, and copper dithiocarbamates, sulfonates, phenates and acetylacetonates. Copper I and II salts and succinic acid or anhydride salts may also be used.

A lubricant composition used according to the invention may contain any type of antioxidant additive known to those skilled in the art.

A lubricant composition used according to the invention may comprise from 0.5% to 2% by weight of at least one antioxidant additive, relative to the total weight of the composition.

Advantageously, the lubricant composition used according to the present invention does not comprise any antioxidant different from the compounds bearing a sterically hindered amine or phenol function as defined according to the invention.

A lubricant composition that is suitable for use in the invention may also comprise at least one detergent additive.

The detergent additives generally make it possible to reduce the formation of deposits on the surface of metal parts by dissolving the oxidation and combustion byproducts.

The detergent additives that may be used in a lubricant composition used according to the invention are generally known to those skilled in the art. The detergent additives may be anionic compounds comprising a long lipophilic hydrocarbon-based chain and a hydrophilic head. The associated cation may be a metal cation of an alkali metal or an alkaline-earth metal.

The detergent additives are preferentially chosen from alkali metal or alkaline-earth metal salts of carboxylic acids, sulfonates, salicylates and naphthenates, and also phenate salts. The alkali metals and alkaline-earth metals are preferentially calcium, magnesium, sodium or barium.

These metal salts generally comprise the metal in a stoichiometric amount or in excess, thus in an amount greater than the stoichiometric amount. They are then overbased detergent additives; the excess metal giving the overbased nature to the detergent additive is then generally in the form of a metal salt that is insoluble in the oil, for example a carbonate, a hydroxide, an oxalate, an acetate or a glutamate, preferentially a carbonate.

A lubricant composition that is suitable for use in the invention may comprise, for example, from 2% to 4% by weight of detergent additive relative to the total weight of the composition.

Also, a lubricant composition used according to the invention may comprise at least one dispersant.

The dispersant may be chosen from Mannich bases, succinimides and derivatives thereof.

A lubricant composition used according to the invention may comprise, for example, from 0.2% to 10% by weight of dispersant(s) relative to the total weight of the composition.

According to a particular embodiment, a lubricant composition used according to the invention is free of dispersant additive of succinimide type.

A lubricant composition that is suitable for use in the invention may also comprise at least one antifoam.

The antifoam may be chosen from silicones.

A lubricant composition that is suitable for use in the invention may comprise from 0.01% to 2% by mass or from 0.01% to 5% by mass, preferentially from 0.1% to 1.5% by mass or from 0.1% to 2% by mass of antifoam, relative to the total weight of the composition.

A lubricant composition that is suitable for use in the invention may also comprise at least one pour-point depressant (PPD).

By slowing down the formation of paraffin crystals, the pour-point depressant additives generally improve the cold-temperature behavior of the composition. Examples of pour-point depressant additives that may be mentioned include polyalkyl methacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes and polyalkylstyrenes.

In particular, a lubricant composition used according to the invention may be free of anticorrosion additive of triazole type and of dispersant additive of succinimide type.

In terms of formulation of such a lubricant composition, said compound(s) bearing a sterically hindered amine or phenol function may be added to a base oil or mixture of base oils, and the other additional additives, including the amine-based and/or sulfur-based antiwear additive(s), are then added.

Alternatively, said compound(s) bearing a sterically hindered amine or phenol function may be added to a pre-existing conventional lubricant formulation, notably comprising one or more base oils, one or more amine-based and/or sulfur-based antiwear additives, and optionally additional additives.

Alternatively, said additive(s) bearing a sterically hindered amine or phenol function according to the invention may be combined with one or more additional additives, and the additive “pack” thus formed is added to a base oil or mixture of base oils.

Advantageously, a lubricant composition used according to the invention has a kinematic viscosity, measured at 100° C. according to the standard ASTM D445, ranging from 1 to 15 mm²/s, in particular ranging from 3 to 10 mm²/s.

Advantageously, a lubricant composition used according to the invention has a kinematic viscosity, measured at 40° C. according to the standard ASTM D445, ranging from 3 to 80 mm²/s, in particular from 15 to 70 mm²/s.

According to an advantageous embodiment of the present invention, the electrical resistivity values measured at 90° C. for the lubricant compositions used according to the invention are between 5 and 10 000 Mohm.m, more preferably between 6 and 5000 Mohm.m.

According to an advantageous embodiment of the present invention, the dielectric loss values measured at 90° C. for the lubricant compositions used according to the invention are between 0.01 and 30, more preferably between 0.02 and 25 and more preferentially between 0.02 and 10.

Advantageously, a lubricant composition used according to the invention may be of a grade according to the SAEJ300 classification defined by the formula (X)W(Y), in which X represents 0 or 5, and Y represents an integer ranging from 4 to 20, in particular ranging from 4 to 16 or from 4 to 12.

According to a particular embodiment, a lubricant composition used according to the invention comprises, or even consists of.

-   -   a base oil or mixture of base oils, preferably chosen from         poly-α-olefins (PAO), polyalkylene glycols (PAG) and esters of         carboxylic acids and of alcohols;     -   one or more compounds bearing a sterically hindered amine or         phenol function, in particular chosen from:     -   aromatic amines, in particular as described previously, notably         diarylaromatic amines, and more particularly diphenylamines,         which are preferably substituted, advantageously in the para         position relative to the amine function, with at least one         C₁-C₁₂ alkyl group;     -   sterically hindered phenols, in particular as defined         previously, and preferably compounds comprising a phenol group,         in which at least one carbon vicinal to the carbon bearing the         alcohol function is substituted with at least one C₁-C₁₀,         preferably C₁-C₆ and notably C₄ alkyl group, in particular         tert-butyl;

and mixtures thereof;

-   -   one or more amine-based and/or sulfur-based antiwear additives,         preferably one or more amine-based and sulfur-based antiwear         additives, more preferentially chosen from compounds of         thia(di)azole type, in particular dimercaptothiazole derivatives         as defined above;     -   optionally one or more additional additives chosen from friction         modifiers, detergents, extreme-pressure additives, antifoams,         pour-point depressant additives, dispersants, antioxidants other         than the compounds bearing a sterically hindered amine or phenol         function according to the invention, and mixtures thereof.

According to a particular embodiment, a lubricant composition used according to the invention comprises, or even consists of:

-   -   from 0.01% to 5% by mass, in particular from 0.1% to 3% by mass         and more particularly from 0.1% to 1% by mass of one or more         compounds bearing a sterically hindered amine or phenol         function, in particular chosen from:     -   aromatic amines, in particular as described previously, notably         diarylaromatic amines, and more particularly diphenylamines,         which are preferably substituted, advantageously in the para         position relative to the amine function, with at least one         C₁-C₁₂ alkyl group;     -   sterically hindered phenols, in particular as defined         previously, and preferably compounds comprising a phenol group,         in which at least one carbon vicinal to the carbon bearing the         alcohol function is substituted with at least one C₁-C₁₀,         preferably C₁-C₆ and notably C₄ alkyl group, in particular         tert-butyl;

and mixtures thereof; and

-   -   from 0.01% to 5% by mass, in particular from 0.1% to 3% by mass         and more particularly from 0.1% to 1% by mass one or more         amine-based and/or sulfur-based antiwear additives, preferably         one or more amine-based and sulfur-based antiwear additives,         more preferentially chosen from compounds of thia(di)azole type,         in particular dimercaptothiazole derivatives,     -   from 60% to 99.9% by mass of base oil(s), preferably chosen from         poly-α-olefins (PAO), polyalkylene glycols (PAG) and esters of         carboxylic acids and of alcohols, and mixtures thereof;     -   optionally from 0.01% to 5% by mass of one or more additives         chosen from friction modifiers, detergents, extreme-pressure         additives, antifoams, pour-point depressant additives,         dispersants, antioxidants other than the compounds bearing a         sterically hindered amine or phenol function according to the         invention, and mixtures thereof;

the contents being expressed relative to the total mass of said lubricant composition.

Application

As indicated previously, a lubricant composition that is suitable for use in the invention as described previously is used as lubricant for a propulsion system of an electric or hybrid vehicle, and more particularly for the motor and the power electronics.

Thus, the present invention relates to the use of a lubricant composition as defined previously, combining one or more compounds bearing a sterically hindered amine or phenol function, in particular as defined previously, and one or more amine-based and/or sulfur-based antiwear additives, preferably dimercaptothiazole derivatives, for lubricating a propulsion system of an electric or hybrid vehicle, in particular for lubricating the electric motor and the power electronics of an electric or hybrid vehicle.

As represented schematically in FIG. 1, the propulsion system of an electric or hybrid vehicle notably comprises the electric motor part (1), an electric battery (2) and a transmission, and in particular a speed reducer (3).

The electric motor typically comprises power electronics (11) connected to a stator (13) and a rotor (14). The stator comprises coils, in particular copper coils, which are powered by an alternating electric current. This makes it possible to generate a rotating magnetic field. For its part, the rotor comprises coils, permanent magnets or other magnetic materials, and is placed in rotation by the rotating magnetic field.

A rolling bearing (12) is generally incorporated between the stator (13) and the rotor (14). A transmission, and in particular a speed reducer (3), makes it possible to reduce the rotation speed at the outlet of the electric motor and to adapt the speed transmitted to the wheels, making it possible simultaneously to control the speed of the vehicle.

The rolling bearing (12) is notably subjected to high mechanical stresses and poses problems of wear by fatigue. It is thus necessary to lubricate the rolling bearing in order to increase its service life. Also, the reducer is subject to high friction stresses and thus needs to be appropriately lubricated in order to prevent it from being damaged too quickly.

Thus, the invention relates in particular to the use of a composition as described previously for lubricating an electric motor of an electric or hybrid vehicle, in particular for lubricating the rolling bearings located between the rotor and the stator of an electric motor.

The invention also relates to the use of a composition as described previously for lubricating the transmission, in particular the reducer, in an electric or hybrid vehicle.

Advantageously, a composition according to the invention may thus be used for lubricating the various parts of a propulsion system of an electric or hybrid vehicle, in particular the rolling bearings located between the rotor and the stator of an electric motor, and/or the transmission, in particular the reducer, in an electric or hybrid vehicle.

Advantageously, as mentioned previously, a lubricant composition according to the invention has excellent antiwear and anticorrosion performance.

According to another of its aspects, the invention also relates to a process for lubricating at least one part of a propulsion system of an electric or hybrid vehicle, in particular the rolling bearings located between the rotor and the stator of an electric motor; and/or the transmission, notably the reducer, comprising at least one step of placing at least said part in contact with a composition as described previously.

The present invention thus proposes a process for simultaneously reducing the wear and corrosion of at least one part of a propulsion system of an electric or hybrid vehicle, in particular the rolling bearings located between the rotor and the stator of an electric motor; and/or the transmission, notably the reducer, said process comprising at least one step of placing at least said part in contact with a composition as described previously.

All of the features and preferences described for the composition used according to the invention and for the uses thereof also apply to this process.

According to a particular embodiment, a composition according to the invention may have, besides lubricating properties, good electrical insulation properties.

According to this embodiment, a composition according to the invention may simultaneously be used for lubricating one or more parts of a propulsion system of an electric or hybrid vehicle, in particular for lubricating the sensors and the solenoid valves of the motor, the rolling bearings, but also the windings located in the rotor and the stator of an electric motor, or else for lubricating the transmission, in particular the gears, the sensors, the solenoid valves or the reducer which are found in an electric or hybrid vehicle, and for electrically insulating at least one part of said propulsion system, notably the battery.

In the context of such an implementation variant, a lubricant composition under consideration according to the invention advantageously has a kinematic viscosity, measured at 100° C. according to the standard ASTM D445, of between 2 and 8 mm²/s, preferably between 3 and 7 mm²/s.

It is understood that the uses described above may be combined, a composition as described previously possibly being used both as lubricant and as electrical insulator, but also as coolant fluid for the motor, the battery and the transmission of an electric or hybrid vehicle.

According to the invention, the particular, advantageous or preferred features of the composition according to the invention make it possible to define uses according to the invention that are also particular, advantageous or preferred.

The invention will now be described with the aid of the examples that follow, which are, needless to say, given as nonlimiting illustrations of the invention.

EXAMPLE

Various compositions were evaluated:

-   -   a composition C1 comprising an amine-based and sulfur-based         antiwear additive of dimercaptothiadiazole type free of additive         bearing a sterically hindered amine or phenol function; and     -   a composition C2 comprising said antiwear additive of         dimercaptothiadiazole type and an additive bearing a sterically         hindered amine function (p,p′-butyloctyldiphenylamine);     -   a composition C3 comprising said antiwear additive of         dimercaptothiadiazole type and an additive bearing a sterically         hindered phenol function (octyl         3,5-di-tert-butyl-4-hyvdroxyhydrocinnamate);

Compositions C1 to C3 comprise, besides the abovementioned compounds, a group V base oil.

The compositions and the amounts (expressed as mass percentages) are indicated in Table 2 below.

TABLE 2 C1 C2 C3 Base oil 99% 98% 98% Dimercaptothiadiazole  1%  1%  1% antiwear agent p,p′- —  1% — Butyloctyldiphenylamine Octyl 3,5-di-tert-butyl-4- — —  1% hydroxyhydrocinnamate

EVALUATION OF THE ANTICORROSION PROPERTIES Evaluation Method

The corrosive (or corroding) power of a composition may be evaluated by means of a test involving study of the variation in the electrical resistance value of a copper wire of a preestablished diameter, as a function of the duration of immersion of this wire in the composition. The variation in this electrical resistance value is directly correlated with the variation in the diameter of the test wire. In the context of the present invention, the diameter of the wire chosen is 70 μm.

In the present case, a copper wire is immersed in a test tube containing 20 mL of a test composition (compositions C2 and C3 being compositions according to the invention and composition C1 being a composition serving as a comparative).

The resistance of the wire is measured using an ohmmeter.

The measuring current is 1 mA.

The temperature of the test composition is brought to 150° C.

The resistance of the copper wire is calculated by this equation (1):

$\begin{matrix} {R = {\rho \times \frac{L}{S}}} & \left\lbrack {{Math}1} \right\rbrack \end{matrix}$

in which R is the resistance, ρ is the resistivity of copper, L is the length of the wire and S is the cross-sectional area.

In this equation (1), ρ and L are constants. Thus, the resistance R is inversely proportional to the cross-sectional area of the immersed wire.

The diameter of the wire is calculated from the cross-sectional area (equation (2)):

$\begin{matrix} {S = {\frac{\pi}{4} \times D^{2}}} & \left\lbrack {{Math}2} \right\rbrack \end{matrix}$

in which D is the diameter of the wire.

Equation (2) is inserted into equation (1) to obtain the relationship between the resistance and the diameter (equation (3)):

$\begin{matrix} {R = {\rho \times \frac{L}{\frac{\pi}{4} \times D^{2}}}} & \left\lbrack {{Math}3} \right\rbrack \end{matrix}$

Thus, when the wire is corroded by the test compositions, the diameter of the wire decreases, thus bringing about an increase in the resistance value.

By monitoring the resistance, it is possible to monitor the change in the diameter of the wire, which reflects the state of corrosion suffered by the immersed wire.

The loss of diameter of the wire is thus calculated directly from the measured resistance.

When the measured resistance is infinite, this is an open circuit. The wire has thus broken, which defines very severe corrosion.

Results

The results are summarized in the following table and are expressed in μm (loss of diameter). The lower the value obtained, the better the anticorrosion properties of the composition evaluated.

A composition is considered to be “noncorrosive” when the loss of diameter of the copper wire studied is less than or equal to 2 μm after immersion for 80 hours, in particular less than or equal to 0.3 μm after immersion for 20 hours in the composition.

TABLE 3 Compositions C1 C2 C3 Loss of diameter (μm) at 0.29 0.01 0.30 20 hours Loss of diameter (μm) at Broken wire 0.69 0.41 40 hours Loss of diameter (μm) at Broken wire 1.28 0.60 60 hours Loss of diameter (μm) at Broken wire 1.85 0.76 80 hours

It emerges from these results that the addition of a compound bearing a sterically hindered amine or phenol function according to the invention makes it possible to reduce the corrosion effects induced by the amine-based and sulfur-based antiwear additive. 

1-10. (canceled)
 11. A method for improving the anti-corrosion properties of a lubricant composition of a propulsion system of an electric or hybrid vehicle, comprising: adding at least one anti-corrosion compound bearing at least one sterically hindered amine or phenol functional group to a lubricant composition for lubricating the propulsion system, the lubricant composition comprising an amine-based anti-wear additive and/or a sulfur-based anti-wear additive.
 12. The method of claim 11, wherein the at least one anti-corrosion compound is chosen from sterically hindered aromatic amines, sterically hindered phenols, or a combination thereof.
 13. The method of claim 11, wherein the at least one anti-corrosion compound is chosen from sterically hindered diarylamine compounds, sterically hindered alkylphenols, or a combination thereof.
 14. The method of claim 11, wherein the at least one anti-corrosion compound is chosen from diarylamine compounds having the following formula: R₆—NH—R₇, wherein R₆ and R₇ are independently chosen from: a phenyl group that is optionally substituted para to the amine function with hydrocarbon-based groups chosen from alkyl or alkenyl groups comprising from 1 to 12 carbon atoms; and a naphthyl group that is optionally substituted para to the amine function with alkyl or alkenyl groups comprising from 1 to 12 carbon atoms.
 15. The method of claim 11, wherein the at least one anti-corrosion compound is chosen from diarylamine compounds having the following formula (I):

wherein R₁ and R₂ are independently chosen from a hydrogen atom, linear or branched alkyl or alkenyl groups comprising from 1 to 12 carbon atoms.
 16. The method of claim 11, wherein the at least one anti-corrosion compound is chosen from diarylamine compounds having the following formula (I′):

wherein R₁ and R₂ are independently chosen from linear or branched C₁ to C₁₂ alkyl groups.
 17. The method of claim 16, wherein R₁ and R₂ are independently chosen from linear or branched octyl or butyl groups.
 18. The method of claim 11, wherein the at least one anti-corrosion compound is chosen from sterically hindered phenols having the formula (II′):

wherein: R¹ and R² are independently chosen from a C₁-C₁₀ alkyl group or a hydroxyl group, with at least one of R¹ and R² representing C₁-C₁₀ alkyl group; n is 1 or 2; each R group is independently chosen from a hydroxyl group or C₁-C₁₀ alkyl groups that are optionally substituted with one or more C₂ to C₁₀ alkoxycarbonyl groups and/or with one or more aryl groups that are optionally substituted with one or more alkyl groups.
 19. The method of claim 18, wherein at least one of R¹ and R² represents a C₄ alkyl group.
 20. The method of claim 11, wherein the at least one anti-corrosion compound is chosen from p,p′-butyloctyldiphenylamine, octyl 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, 2,6-di-tert-butylphenol, or a combination thereof.
 21. The method of claim 11, wherein the amine-based anti-wear additive and/or the sulfur-based anti-wear additive is chosen from 2,5-dimercapto-1,3,4-thiadiazole derivatives having the following formulae, taken alone or in combination:

wherein: each R₁ group is independently selected from a hydrogen atom, a linear or branched alkyl or alkenyl group comprising from 2 to 18 carbon atoms, or an aromatic substituent; and each n is independently selected from 1, 2, 3, or
 4. 22. The method of claim 21, wherein: each R₁ group is independently selected from a hydrogen atom, linear or branched alkyl or alkenyl groups comprising from 8 to 12 carbon atoms or aromatic substituents; and n is
 1. 23. The method of claim 11, wherein, relative to the total mass of the lubricant composition: the at least one anti-corrosion compound is present in an amount ranging from 0.01% to 5% by mass; and/or the amine-based and/or sulfur-based anti-wear additive is present in an amount ranging from 0.01% to 5% by mass.
 24. The method of claim 23, wherein, relative to the total mass of the lubricant composition: the at least one anti-corrosion compound is present in an amount ranging from 0.1% to 1% by mass; and/or the amine-based anti-wear additive and/or the sulfur-based anti-wear additive is present in a content ranging from 0.1% to 1% by mass.
 25. A method of reducing corrosion in a propulsion system of an electric or hybrid vehicle, comprising lubricating an electric motor and/or power electronics of the electric or hybrid vehicle with a lubricant composition comprising: at least one anti-corrosion compound bearing at least one sterically hindered amine or phenol functional group; and an amine-based anti-wear additive and/or a sulfur-based anti-wear additive.
 26. The method of claim 25, wherein: the at least one anti-corrosion compound is chosen from sterically hindered diphenylamine compounds, sterically hindered alkylphenol compounds, or a combination thereof; and the amine-based anti-wear additive and/or the sulfur-based anti-wear additive is a 2,5-dimercapto-1,3,4-thiadiazole derivative.
 27. The method of claim 25, further comprising lubricating rolling bearings located between a rotor and a stator of the electric motor with the lubricant composition.
 28. The method of claim 25, further comprising lubricating a transmission of the electric or hybrid vehicle with the lubricant composition. 